It has long been recognized that the normal human eye is not a perfect dioptric system, where there exists aberration to some extent, which degrades retinal imaging quality and limits visual sensitivity. Except that spherical mirror and cylindrical mirror can be corrected by some devices, such like spectacles, contact lenses, etc, the higher-order aberration, such as coma, spherical aberration, etc, still can't be corrected accurately and effectively by devices.
In 1962,Smirnov advanced higher-order aberration features of eyes firstly, and indicated that the aberration of human eyes could be corrected by individualized lenses. David Williams Lab has done some related experiments on the higher-order aberration correction of human eyes, which proved that if the higher-order aberration had been corrected, it would be helpful for improving image subjective quality (“Visual Performance after correcting the monochromatic and chromatic aberrations of the eye” Geun-Young Yoon and David R. Williams, J. Opt. Soc. Am. A/Vol. 19, No. 2/February). In 1994, Liang et al were firstly reported to measure the general aberration of dioptric system of human eyes with the use of a Hartmann-Shack wavefront sensor. (“Objective measurement of wavefront aberrations of the human eye with the use of a Shack-Hartmann wavefront sensor” J. Liang, B. Grimm and S. Goelx, et al, J. Opt. Soc. Am. A, 1994, 11:1949-1957). In 2005, the Adaptive Optics Lab of the Institute of Optics and Electronics the Chinese Academy of Science applied the patent, “Vision simulation system for binocular stereoscopic higher-order aberration correction” (Publication number CN 1689538A), in which they made out a device that can measure the higher-order aberration of human eyes exactly and established the foundation of higher-order aberration correction of human eyes. Subsequently, the Institute of Optics and Electronics the Chinese Academy of Science proposed a method of higher-order aberration correction of human eyes in the patent, “Correction method for higher-order aberration of human eyes” (Publication number CN 1702494A). Based on the analysis of various previous methods on higher-order aberration correction of human eyes, the method of aberration correction of human eyes in the way of individualized lenses is without doubt the securest, most convenient, and most economical.
However in the practical applications, there are still some problems in the manufacture of the individualized lenses which can be marketized.
(1) Based on the detected contribution of each order aberration to correction, continuous embossment microstructure needs to be made on the materials, which requirement is not easy to satisfy by the ordinary manufacturing means;
(2) The higher-order aberrations are different greatly from various human eyes, so higher-order aberration correction has no such generalization as lower-order aberration correction. Correction for higher-order aberration needs to detect the contribution of each order aberration to correction corresponding to different individual human eyes, and on the system with the corrected lower-order aberration, creates continuous embossment microstructure in the way of optical lithography, and compensates the detected aberration to make the system be an individual one, which can correct low-order and higher-order aberration at the same time. However, the construction of the mask of traditional lithography is fixed, poorly flexible, and costly, so that it can't satisfy the requirements of devices on individualization.
So in the manufacture of individualized lenses, maskless lithography technology has great superiority without doubt. Besides, in the aspect of maskless lithography technology, in 2005, ASML Ltd. in Netherlands won the invention patent, “System and method for maskless lithography using spatial light modulator array” ( publication number CN 1573561A), in which Spatial Light Modulator Array is applied, and the incidence uniform light is amplitude modulated, and the corresponding gray images is obtained, which is projected to planar object (including semiconductor wafer, glass substrate, and so on), and then the exposure is completed. However, since the made-out contact lenses needs to be worn close to eyeball and the correction of general diopter must be considered, this kind of lenses have to be spherical. That means continuous embossment microstructure should be etched on a sphere, not on an ordinary lithographic plane. But the technology in the patent of ASML can't resolve this problem of projection lithographic on the spherical surface.